Variable displacement fluid translating device

ABSTRACT

An axial piston type fluid energy translating device has fluid passages in the pistons, shoes, swash plate and cam member to conduct fluid from the high pressure port to pockets on the back of the cam member adjacent the cam support. The high pressure fluid in the pockets counter-balances the force applied to the swash plate and cam member by the pistons exposed to high pressure fluid.

United States Patent Adams et al.

[ 1 Aug. 12, 1975 VARIABLE DISPLACEMENT FLUID TRANSLATING DEVICE [75]Inventors: Cecil E. Adams; Ellis H. Born; Gary C. Smith, Jr., all ofColumbus, Ohio [73] Assignee: Abex Corporation, New York, NY.

[22] Filed: Jan. 31, 1974 [21] Appl. No.: 438,311

[52] US. Cl. 91/488 [51] Int. Cl. F04b 1/00 [58] Field of Search 91/485,486, 487, 488, 91/499 [56] References Cited UNITED STATES PATENTS2,699,123 l/1955 Bonnette 91/488 2,871,798 2/1959 Thoma 91/489 3,124,0083/1964 Firth 91/506 3,173,376 3/1965 l-Iulman 91/488 3,650,180 3/1972Gantschnigg 91/488 3,682,044 8/1972 Ankeny 91/487 3,779,137 12/1973Koivunen 91/489 3,783,743 l/1974 Raymond 91/488 FOREIGN PATENTS ORAPPLICATIONS 883,348 7/1943 France 91/485 Primary Examiner-William L.Freeh Assistant Examiner-G. P. LaPointe Attorney, Agent, or Firm-ThomasS. Baker, Jr David A. Greenlee [5 7 ABSTRACT An axial piston type fluidenergy translating device has fluid passages in the pistons, shoes,swash plate and cam member to conduct fluid from thehigh pressure portto pockets on the back of the cam member adjacent the cam support. Thehigh pressure fluid in the pockets counter-balances the force applied tothe swash plate and cam member by the pistons exposed to high pressurefluid.

4 Claims, 7 Drawing Figures PATENTED AUG 1 2 I975 SHEET PATENTEU AUG 121975 SHEET 1 VARIABLE DISPLACEMENT FLUID TRANSLATING DEVICE BACKGROUNDOF THE INVENTION 1. Field of the Invention The instant invention relatesto a variable displacement fluid translating device of the axial pistontype and more particularly to a means for counterbalancing andlubricating a cam member of such a device.

2. Description of the Prior Art A common type of variable displacementfluid translating device such as an axial piston pump or motor has arotating barrel with a plurality of axially aligned cylinders. A pistonconnected at one end by a shoe to an angled swash plate is received ineach of the cylinders and reciprocates as the barrel is rotated and theshoe slides along the swash plate. The stroke of the piston iscontrolled by the angularity of the swash plate and deter mines thevolume of fluid displaced by the fluid translating device hereinafterreferred to as a pump.

In one form of pump, the swash plate is supported by a cam member whichpivots in a cam support about an axis perpendicular to the rotationalaxis of the barrel in order to change the volume of fluid displaced bythe pump. During operation of the pump the cylinders and pistons in thebarrel alternately connect with low and high pressure ports. As thepistons are exposed to the high pressure port, a large force istransmitted from the fluid through the pistons and shoes to the cammember. This large force becomes troublesome when it is desired to pivotthe cam member in order to change the displacement of the pump. Theforce causes a great deal of friction between the cam member and the camsupport which must be overcome before the cam member can pivot.

One means of reducing the friction between the cam member and itssupport is to coat one of the surfaces with a material which has a lowcoefficient of friction. However, it has been found that coated surfaceserode after heavy use and friction between the cam member and the camsupport begins to increase.

Another means for reducing the friction between the cam member and thecam support is to connect fluid in the high pressure port with the spacebetween the cam member and the cam support. In U.S. Pat. No. 3,682,044,an exterior hydraulic line is run from the high pressure port to acompensator block which connects the high pressure fluid with passagesleading to holes in the cam support which holes communicate with the cammember. The effect of this high pressure fluid is to counterbalance someof the force applied by the pistons on the cam member and to lubricatethe contacting cam member and cam support surfaces to reduce thefriction between the surfaces and thereby reduce the force required topivot the cam member relative to the cam support.

A disadvantage of connecting high pressure fluid to apertures positionedin the cam support is that the fluid is not always communicated to thepoint of maximum force between the cam member and the cam support. Thisis because the forces applied to the cam member act along a lineperpendicular to the face of the cam member which receives the pistons.As the cam member is pivoted in the cam support, this force is directedthrough the cam member and acts on different portions of the camsupport.

It is desirable to supply high pressure counterbalancing fluid betweenthe cam member and the cam support which is at all times opposite theforce applied to the cam member by the pistons.

SUMMARY OF THE INVENTION It is an object of this invention to provide avariable displacement fluid translating device in which the forcesapplied by the pistons on the cam member are counterbalanced by a pocketof high pressure fluid acting opposite the position at which the pistonsare applying the force to the cam member.

It is another object of the instant invention to provide a variabledisplacement fluid translating device in which high pressure fluid isconducted through the pistons, the shoes and the cam member to pocketson the surface of the cam member adjacent the cam support in order toreduce the friction between the cam member and support.

Other objects of the invention will appear hereinafter, the novelfeatures and combinations being set forth in the claims. In the variabledisplacement axial piston pump of the instant invention, high pressurefluid in the barrel cylinders is fed through the pistons, the shoes, theswash plate and the cam member to pockets formed on the back surface ofthe cam member adjacent the cam support. The pockets are substantiallyaligned with the surfaces on the cam member to which the forces areapplied by the pistons. Feeding the high pressure fluid through passagesformed in the piston, the shoes, the swash plate and the rocker cameliminates external hydraulic lines from the high pressure port to thecam support.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial section of a portion ofthe fluid energy translating device of this invention.

FIG. 2 is a view of the flat surface of the cam member adjacent theswash plate.

FIG. 3 is view of the back surface of the cam member which pivots withinthe cam member.

FIG. 4 is a view of the swash plate taken along the line 4-4 on FIG. 1.

FIG. 5 is a view similar to that of FIG. 4 with the number of aperturesin the swash plate changed.

FIG. 6 is a view similar to that of FIG. 4 with the number of aperturesin the swash plate changed.

FIG. 7 is a view similar to that of FIG. 4 with the number of aperturesin the creep plate changed.

DESCRIPTION OF THE PREFERRED EMBODIMENT The axial piston pump 10 of theinstant invention has a casing which includes an outer cylindrical body12 and an end cap 13. The end cap 13 is attached to the body 12 byfastening means not shown. The casing forms an internal cavity 15 whichhouses the operating mechanism of the pump 10. l

A barrel 16 is rotatably mounted in a roller bearing 17 in body 12.Bearing 17 is located in body 12 by a shoulder 18 and a retaining ring19 which is urged against bearing 17 by end cap 13. An oil seal 20prevents fluid seepage at the joint between body 12 and end cap 13.

A prime mover not shown drives barrel 16. The prime mover is attached toone end of a shaft 22 which is coupled to barrel 16 by splines 23. Shaft22 is restrained from moving axially relative to barrel 16 by a bolt 24which passes through a spring 25, a retainer 26 and is threaded intoshaft 22. Clearance between bolt 24 and retainer 26 permits limitedaxial movement of shaft 22 relative to barrel 16.

Within barrel 16 are formed a plurality of cylinders 28 which arealigned parallel with the axis of rotation of barrel 16. The cylinders28 are equally spaced from each other within barrel l6 and are displacedradially from the axis of rotation an equal distance. Positioned withineach cylinder 28 is a hollow piston 29.

At one end of each piston 29 is a shoe 30 which is attached to a swashplate 31 by a means of a shoe retainer assembly 32. When barrel 16 isrotated, the shoes 30 slide over swash plate 31 and reciprocate thepistons 29 in the cylinders 28 to thereby pump fluid.

The shoe retainer assembly 32 maintains shoes 30 in contact with swashplate 31. The assembly 32 comprises a shoe retainer plate 34 which has aplurality of openings 35 which are of sufficient diameter to pass over apiston 29 and engage a shoulder 36 on each shoe 30. A bolt 38 drawsretainer plate 34 towards swash plate 31 to clamp the shoes 30therebetween. Bolt 38 passes through a retainer washer 39, a socketmember 41, cam member 37, a spring 44, a spring retainer 45, and has acastle nut 46 turned on the end thereof. Spring 44 prevents springretainer 45 from contacting cam member 37 and enables retainer plate 34to move slightly in response to a high axial force on bolt 38. Thisallows piston shoes 30 to .move away from swash plate 1 31 slightly andride on a, fluid cushion therebetween.

Cam member 37 is pivotally mounted in a cam support 50. When cam member37 is moved relative to cam support 50, the stroke of the pistons 29 ischanged and thereforethe displacement of pump is changed. One means ofpivoting cam member 37 is a double headed piston 55 which is connectedto cam member 37 by means of a bifurcated arm 52.

When rocker cam .37 is pivoted such that swash plate 31is'perpendicularto shaft 22, there is no reciprocating'mov'ements ofpistons 29 when barrel 16 is rotated and pump 10 is operating at itsminimum fluid displacement when barrel 16 is rotated. When rocker cam 37is pivoted such that swash plate 31 is angled its greatest amount, thepistons 29 move through their greatest stroke and pump 10 is operatingat its maximum fluid displacement when barrel 16 is rotated.

When barrel 16 is rotated and pump 10 is displacing fluid, the pistons29 are alternately exposed to high and low pressure ports in a'portplate 58. The pressure in the high pressure port may be on the order ofseveral thousand pounds per square inch. This force in transmittedthrough the piston 29 and its shoe 30 to the swash plate 31. The forceon the swash plate 31 acts to urge the cam member 37 against the camsupport 50. This creates a large amount of friction which must beovercome when cam member 37 pivots relative to cam support 50.

In order to reduce the friction between the cam member 37 and the camsupport 50, high pressure fluid is routed to a pocket 71 in the rearface 59 of cam member 37 to counterbalance the force applied to theswash plate 31. Pocket 71 is best seen in FIG. 3.

High pressure fluid flows through bore 61 in piston 29, a bore 62 inshoe 30 and into a cavity 63 adjacent swash plate 31. Swash plate 31 hasa plurality of circumferentially arranged passages 65 extendingtherethrough as seen in FIGS. 1 and 4 through 7. Each passage 65 is incommunication with a shallow metering groove 66 formed on the bottomside of swash plate 31 adjacent cam member 37.

As seen in FIG. 2, a pair of ports 67 are formed in rocker cam 37 toreceive fluid which feeds from the grooves 66. One port 67 is alignedwith the grooves 66 and passages 65 which receive fluid from pistonsexposed to the high pressure port and the other port 67 is aligned withthe grooves at 66 and passages 65 which receive fluid from the pistonsexposed to the low pressure port of the pump.

Since only one pump port at a time will conduct high pressure fluid,only one port 67 at a time will receive high pressure fluid.

A bore 70 extending from the top surface 68 of rocker cam 37 to the rearface 59 conducts fluid in the port 67 to the pocket 71. When the highpressure fluid collects in pocket 71 it resists the force applied toswash plate 31 by pistons 29 as they are exposed to the high pressureport. The fluid in pocket 71 also lubricates the face 57 on cam support50 and face 59 on cam member 37 to reduce the friction therebetween.

Since pocket 71 is formed in face 59 on the movable cam member 37, thehigh pressure fluid is acting at a point directly opposite where forcefrom the high pressure fluid is being applied by pistons 29 to the swashplate 31 or any angular position of cam member 37 in cam support 50.

High pressure fluid is normally fed from the shoes 30 to the passages 65in grooves 66 to a port 67. However, when a passage 65 in the swashplate 31 is uncovered, by rotation of the shoes 30 fluid under pressurein the port 67 will leak back through grooves 66 to the uncoveredpassages 65. Since the passages 65 are only uncovered for a short time,only a small amount of fluid will flow back therethrough. The amount offluid flowing back through is further reduced because the cross sec-'tional area of a groove 66 is much smaller than that of a passage 65.The small grooves 66 also prevent a large amount of fluid from flowingfrom the cavities 63 under shoes 30 which would drain the fluid requiredto provide a fluid film between the shoes 30 and the creep plate 31.

It is important that high fluid pressure in port 67 be maintained inorder to maintain the pressure of the counterbalancing fluid in thepocket 71. This is only possible if at any moment the majority of thepassages 65 which connect to a port 67 are being fed fluid at highpressure or are blocked. Consequently, spacing of the passages 65 iscritical.

Refering to FIG. 4, it has been found that. it is undesirable to havethe number of passages 65 equal to the number of pistons 29 in the pump10 or equal to any multiple thereof. With this number of passages 65 itis possible that all of the passages 65 could be uncovered at one timeand consequently no high pressure fluid would be supplied to port 67.FIG. 5 shows that with a number of passages 65 equal to double thenumber of pistons 29 that at times half of the passages 65 would beuncovered, and consequently, a majority of passages 65 would not befeeding high pressure fluid to the port 67.

FIG. 6 shows a creep plate 31 which has eight passa'ges 65 and FIG. 7shows a creep plate 31 which has twelve passages 65. When these creepplates 31 are used with a pump having seven pistons 29, and shoes 30there are more passages 65 feeding high pressure fluid or blocking theescape of this fluid from port 67 than there are passages open andproviding a means of escape to the high pressure fluid.

In FIG. 7, it can be seen that passages 65 are equally spaced from eachother and distance along the arc of the circle on which all passages 65lie between the farthest outside edges of two adjacent passages 65 isless than the outside diameter of a shoe 30. Consequently, a single shoe30 may overlie two passages 65.

Obviously, those skilled in the art may make various changes in thedetails and arrangements of parts without departing from the spirit andsculp of the invention as it is defined by the claims hereto appended.Applicant, therefore, wishes not to be restricted to the pre ciseconstruction hereindisclosed.

Having thus described and shown an embodiment of the invention, what isdesired to secure by Letters Patent of the United States is:

1. A variable displacement fluid energy translating device comprising: abody; a barrel rotatably mounted within the body; a plurality ofcylinders formed in the barrel; a piston within each cylinder; a camsupport in the body; a cam member mounted on the cam support andpivotable relative to the support; a swash plate having a top surfaceand a bottom surface and mounted on the cam member; a shoe pivotablyattached to each piston adapted to slide on the top surface of the swashplate and reciprocate the piston within a cylinder when the barrel isrotated; means for pivoting the cam member from a position causingmaximum fluid flow in one direction through the translating device to aposition causing maximum fluid flow in another direction; a bore in eachpiston for conducting fluid under pressure in the cylinder through eachpiston to its shoe; a second bore in each shoe which feeds fluid fromthe piston through the shoe to a space between the bottom of the shoeand the top surface of the swash plate to hydraulically balance theshoe; a plurality of apertures in the swash plate for conducting fluidfrom the bottom of each shoe through the swash plate; a first collectorport for collecting fluid under pressure from some of the swash plateapertures when the device is causing fluid flow in one direction, asecond collector port for collecting fluid under pressure from other ofthe swash plate apertures when the device is causing fluid flow in theother direction, the first and second collector ports being isolatedfrom one another, a third bore in the cam member for conducting fluidfrom the first collector port through the cam member; a first pocket onthe back of the cam member connected to the third bore for receiving thefluid from the first collector port; a fourth bore in the cam member forconducting fluid from the second collector port through the cam member;a second pocket on the back of the cam member connected to the fourthbore for receiving fluid from the second collector port; wherein thefluid under pressure in one of the first and second pocketssubstantially reduces the friction between the cam member and the camsupport and applies a force on the cam member which resists the forceapplied by the pistons on the swash plate.

2. The variable displacement fluid energy translating device recited inclaim 1, including restrictor means positioned between the swash plateapertures and the collector ports to limit the amount of pressure fluidthat flows out of uncovered swash plate apertures from the collectorports and to maintain the hydraulic balance on the shoes.

3. A variable displacement fluid energy translating device comprising: abody; a barrel rotatably mounted within the body; a plurality ofcylinders formed in the barrel; a piston within each cylinder; a camsupport in the body; a cam member mounted on the cam support to form abearing pivotable relative to the support; a swash plate having a topsurface and a bottom surface and mounted on the cam member; a shoepivotably attached to each piston and slideable on the top surface ofthe swash plate to reciprocate the pistons within the cylinders when thebarrel is rotated; means for pivoting the cam member from a position ofminimum displacement of the translating device to a position of maximumdisplacement of the translating device; a bore in each piston forconducting fluid under pressure in the cylinder through each piston toits shoe; a second bore in each shoe which feeds fluid from the pistonthrough the shoe to a space between the bottom of the shoe and the topsurface of the swash plate to provide pressure fluid beneath the shoe tosubstantially hydraulically balance the shoe in opposition to the thrustof the piston; a plurality of apertures in the swash plate forsequentially conducting fluid from the bottom of each shoe through theswash plate; a collector port; fluid restrictor means connecting theswash plate apertures and the collector port and limiting the rate offluid flow from an uncovered aperture to maintain pressure fluid beneatheach shoe; a third bore in the cam member for conducting fluid from thecollector port through the cam member; a pocket on the back of the cammember for receiving the fluid from the third bore to lubricate thebearing surfaces between the cam support and cam member wherein thefluid in the pocket applies a counter-acting force on the cam memberwhich resists the force applied by the pistons and shoes on the swashplate.

4. The variable displacement fluid translating device recited in claim 3wherein the fluid restrictor means comprises a plurality of shallowgrooves formed on the bottom surface of the swash plate and the shallowgrooves are angled with respect to the apertures in the swash plate.

1. A variable displacement fluid energy translating device comprising: abody; a barrel rotatably mounted within the body; a plurality ofcylinders formed in the barrel; a piston within each cylinder; a camsupport in the body; a cam member mounted on the cam support andpivotable relative to the support; a swash plate having a top surfaceand a bottom surface and mounted on the cam member; a shoe pivotablyattached to each piston adapted to slide on the top surface of the swashplate and reciprocate the piston within a cylinder when the barrel isrotated; means for pivoting the cam member from a position causingmaximum fluid flow in one direction through the translating device to aposition causing maximum fluid flow in another direction; a bore in eachpiston for conducting fluid under pressure in the cylinder through eachpiston to its shoe; a second bore in each shoe which feeds fluid fromthe piston through the shoe to a space between the bottom of the shoeand the top surface of the swash plate to hydraulically balance theshoe; a plurality of apertures in the swash plate for conducting fluidfrom the bottom of each shoe through the swash plate; a first collectorport for collecting fluid under pressure from some of the swash plateapertures when the device is causing fluid flow in one direction, asecond collector port for collecting fluid under pressure from other ofthe swash plate apertures when the device is causing fluid flow in theother direction, the first and second collector ports being isolatedfrom one another, a third bore in the cam member for conducting fluidfrom the first collector port through the cam member; a first pocket onthe back of the cam member connected to the third bore for receiving thefluid from the first collector port; a fourth bore in the cam member forconducting fluid from the second collector port through the cam member;a second pocket on the back of the cam member connected to the fourthbore for receiving fluid from the second collector port; wherein thefluid under pressure in one of the first and second pocketssubstantially reduces the friction between the cam member and the camsupport and applies a force on the cam member which resists the forceapplied by the pistons on the swash plate.
 2. The variable displacementfluid energy translating device recited in claim 1, including restrictormeans positioned between the swash plate apertures and the collectorports to limit the amount of pressure fluid that flows out of uncoveredswash plate apertures from the collector ports and to maintain thehydraulic balance on the shoes.
 3. A variable displacement fluid energytranslating device comprising: a body; a barrel rotatably mounted withinthe body; a plurality of cylinders formed in the barrel; a piston withineach cylinder; a cam support in the body; a cam member mounted on thecam support to form a bearing pivotable relative to the support; a swashplate having a top surface and a bottom surface and mounted on the cammember; a shoe pivotably attached to each piston and slideable on thetop surface of the swash plate to reciprocate the pistons within thecylinders when the barrel is rotated; means for pivoting the cam memberfrom a position of minimum displacement of the translating device to aposition of maximum displacement of the translating device; a bore ineach piston for conducting fluid under pressure in the cylinder througheach piston to its shoe; a second bore in each shoe which feeds fluidfrom the piston through the shoe to a space between the bottom of theshoe and the top surface of the swash plate to provide pressure fluidbeneath the shoe to substantially hydraulically balance the shoe inopposition to the thrust of the piston; a plurality of apertures in theswash plate for sequentially conducting fluid from the bottom of eachshoe through the swash plate; a collector port; fluid restrictor meansconnecting the swash plate apertures and the collector port and limitingthe rate of fluid flow from an uncovered aperture to maintain pressurefluid beneath each shoe; a third bore in the cam member for conductingfluid from the collector port through the cam member; a pocket on theback of the cam member for receiving the fluid from the third bore tolubricate the bearing surfaces between the cam support and cam memberwherein the fluid in the pocket applies a counter-acting force on thecam member which resists the force applied by the pistons and shoes onthe swash plate.
 4. The variable displacement fluid translating devicerecited in claim 3 wherein the fluid restrictor means comprises aplurality of shallow grooves formed on the bottom surfaCe of the swashplate and the shallow grooves are angled with respect to the aperturesin the swash plate.